Heavy ion radiotherapy is generally administered using a particle accelerator and a beam delivery system. The beam delivery system often contains a medical gantry, which combines the bending magnets and the focusing magnets for the particle beam in a single assembly. In order to significantly decrease the weight and/or size of the gantry (often by an order of magnitude), the use of superconducting magnets has been proposed. Such superconducting medical gantries use iron yokes, which serve both to amplify the magnetic field in the bore of the magnet and to shield the vicinity from the magnetic field. Shielding is also important to protect patients (particularly those with pacemakers and other electronic implants), as well as to minimize interference with nearby electronic sensors or other components near the gantry or near the patient.
However, the use of iron destroys the linearity of the magnetic field, e.g., the magnetic field would no longer increase linearly with current, such as in the high field range. The use of iron also introduces magnetic hysteresis and eddy currents in the iron, which further complicate effective treatment. For example, the magnetic field may need to be changed during the treatment procedure, and this can be more difficult due to hysteresis effects and eddy currents in the iron. Thus, it is desirable to develop medical gantries which mitigate these downsides.
Ironless medical gantries can restore the linearity lost in medical gantries containing iron yokes. Ironless medical gantries can also reduce the weight of the gantry compared with medical gantries containing iron yokes. However, ironless gantries can require significantly more current than gantries containing iron yokes. Ironless gantries can also be limited to generating a dipole field moment and are more sensitive to the size and shape of the associated particle beam. As a result, ironless gantries can also complicate effective treatment.
Thus, it may be desirable to develop new superconducting medical gantries that are ironless, yet that do not necessarily suffer from the above-noted possible drawbacks with conventional ironless gantries. The systems and methods disclosed herein may mitigate or eliminate one or more of such drawbacks.